This invention relates to dunnage bags for use in shipment of freight by rail, ship, truck, aircraft, and the like, and more particularly, to an inflatable, disposable dunnage bag for such use. Typically, such dunnage bags have a gastight bladder (usually polyethylene) surrounded by an outer protective and supportive shroud consisting of a number of plies of heavy paper.
The inflatable, disposable dunnage bags are used in freight carriers where it is customary to fill the spaces between the cargo or between the cargo and walls of the freight carrier to prevent the cargo from shifting and damaging either the cargo itself and/or the walls of the freight carrier. Inflatable, disposable dunnage bags are placed between the cargo in a deflated condition and are subsequently inflated with high pressure air to a certain design pressure, usually between 2 and 6 pounds per square inch, depending on the size and wall structure of the particular bag.
Experience with this type of dunnage bag has revealed that the multi-ply paper shroud structure must function to support the inflated bladder under conditions of inflation and shock loading. Obviously, the end closures of the bag must be made strong enough to prevent their failure under these conditions. To this end, a number of end fold closure designs have been proposed and tried in the past.
Typical of recent end closure designs for dunnage bags are those described in the U.S. Pats. to Ludlow, No. 3,365,116; to Hollis, No. 3,556,318; to Evans, No. Re. 27,787; to Shaw No. 3,808,981; and to Baxter, No. 3,955,690. The end closures illustrated in all of these patents involve the use of flaps on the plies of one wall which are folded over the end of the bag and then placed between certain plies of the opposite wall of the dunnage bag. Certain of these folded flaps are then secured to each other and/or adjacent plies of the wall into which they have been inserted.
Fabrication of such a dunnage bag necessarily requires a number of steps to fold over the flaps, in the proper sequence, and secure them (as with adhesive) to specific adjacent flaps of plies of the wall into which they are inserted.
In order that a multi-ply dunnage bag can be fabricated efficiently and hence, less expensively, it would be desirable to incorporate an end closure arrangement which would be relatively simple to fabricate, preferably one in which only a relatively small number of steps are required to form the completed end closure. However, such an arrangement must also provide for strong end closure joints having a fairly even distribution of stress throughout the end closure assembly.